200 



PHYLUM V. PHAEOPHYCEAE 



304. Among the commonest of the smaller Brown Algae 

 are the species of Ectocarpus in which the plant body is 

 composed of simple or branched filaments which may 



attain a length of many centimeters. They 

 are firmly rooted below, and their tufted 

 filaments float as dark brown masses in the 

 tide currents near the shore. They are 

 propagated by zoospores produced in one- 

 celled sporangia which occur on the sides 

 of the filaments. These zoospores are 

 oval, pointed anteriorly, and have two 

 long cilia which are attached near together at one side. 

 Generation takes place by the union of isogametes, re- 

 sembling the zoospores, but originating in many-celled 

 sporangia (gametangia) also occurring on the sides of the 

 filaments. This union takes place in the water after 

 both gametes have escaped from the sporangia, and it 

 results in the formation of a zygote, which soon germi- 

 nates and gives rise to a new plant. 



305. The Kelps (Laminariacece) while large massive 

 plants are still of a low type. In the Flat Kelps, or 

 Devil's Aprons (Laminaria), there is a stout stem a cen- 

 timeter or so thick, and a decimeter to nearly a meter 

 long, firmly rooted below, and flat- 

 tened into a broad "leaf" above. 

 The whole plant may be a meter or 

 even several meters in length, and 

 the "leaf" a few centimeters to half 

 a meter in breadth. On the sur- 

 face of the "leaf" there develop 

 patches of 1-celled sporangia that produce zoospores 

 like those in Ectocarpus. Gametes are not certainly 

 known to occur in the Kelps. 



306. Other kelps that are common on the Atlantic or 



Fig. 86. — Laminaria. 



